1. Field of the Invention
This invention relates in general to the field of applicators for applying an adhesive and in particular to apparatus for applying multiple lines of adhesives in commercialized, assembly-line operations.
2. Description of the Prior Art
In commercial applications, where an adhesive is applied to various products such as paper cartons, diapers, paper towels, bathroom tissue, or other like products, it is typical that automatic adhesive spray applicators be used to apply the adhesive. In such applications, the adhesive may be in the form of small dots, thin dashed or solid lines, large dots, or broad dashed or solid lines. The lines or dots are usually applied in a direction coincident with the direction of travel of the product as it travels past the fixed position of the adhesive applicator. In the event a series of multiple parallel lines or dots of adhesive are required to be applied, a number of adhesive applicators may be "ganged" together.
In the early history of the prior art, the adhesive applicators were air actuated whereby a built-in air cylinder is used to lift a shutoff needle from a seat to permit the dispensing of a pressurized adhesive. Air-operated actuators have been found to be inherently disadvantageous in applying adhesives in commercial applications. For example, they are not sufficiently responsive for high-speed production where their use results in misapplication of the amount of the adhesive and mislocation of the placement of the adhesive. If the adhesive is misplaced or applied at the wrong location, the product may be spoiled and perhaps be rejected as unsatisfactory. Similarly, if insufficient adhesive is applied, the glued joint may be weaker than required. If an attempt is made to overcome an insufficiency of adhesive by applying additional adhesive at additional locations where such additional locations are not critical to the product, the cost of such additional adhesive may unnecessarily and materially add to the cost of production. Thus, for every application there is an optimum condition of applying the exact amount of adhesive at the desired location. Such applications require apparatus which dispenses an adhesive and which responds accurately and repeatedly to input control signals.
Attempts have been made to overcome the inherent disadvantages in air-operated applicators by the use of sophisticated electronic equipment to operate solenoid valves for purposes of controlling the air used to operate the applicator; however, such attempts have not in general been satisfactory. Electronic control of the air still resulted in a time delay between the operation of the valve and the subsequent operation of the air cylinder of the applicator. The time delay is not consistent and will vary inasmuch as sealing packings within the applicator change characteristics with heat and use causing inconsistencies in application of the adhesive when responding to the same signal.
The use of airless, solenoid-operated adhesive spray applicators have substantially overcome the problems of the air-operated applicators. In such applicators, the adhesive is applied without the use of compressed air. Upon activation, a solenoid unseats a spring-loaded plunger which then permits a pressurized adhesive to flow past the valve and onto the product. The airless, solenoid-operated applicator shown and described in U.S. Pat. No. 3,212,715, issued Oct. 19, 1965, by Eric H. Cocks, and its progeny have been shown to be immensely successful in overcoming the problems associated with air-actuated applicators.
The need for stronger, adhesively-bonded joints and/or smaller applications of an adhesive brought about the use of hot-melt adhesives as contrasted with cold adhesives which are in a liquid form at room temperature. Hot-melt adhesives liquify when heated from 200.degree. F. to 500.degree. F; at room temperature they are in a solid form. The aforementioned problems associated with air-actuated applicators became more acute with their use with hot-melt adhesives. The heat needed to maintain the glue in a liquid state prior to and during dispensing made the operation of the air-actuated applicators even more erratic. On the other hand, the airless, solenoid-operated applicator, invented by Eric H. Cocks, was quite adaptable for use with hot-melt adhesives. U.S. Pat. Nos. 3,485,417, issued Dec. 23, 1969, "Hand-Held Applicator for Hot-Melt Adhesives", 3,408,008, issued Oct. 29, 1968, "Apparatus for Applying Hot-Melt Adhesives", and 3,662,927, issued May 16, 1972, "Hot-Melt Adhesive Systems", all by Eric H. Cocks, disclose some of the innovations that Mr. Cocks has made in the field of hot-melt adhesive applicators and apparatus associated therewith and are typical of the state of the prior art.
As might have been expected, the commercialization of the use of adhesives continued to grow. Such growth has, in part, been brought about by the improvements in the equipment used to dispense the glue as previously described in my United States patents relating thereto. Presently, applications involving closely-spaced, multiple lines or dots of adhesive are being used with increasing frequency. And, as might also have been expected, it is desirable in these applications to obtain the benefits of a hot-melt adhesive.
In attempting to provide apparatus to fulfill the requirements associated with multiple-line applications, a number of single applicators have been "ganged" and in another attempt, multiple dispensing heads have been adapted to a single applicator. Neither prior-art attempted solution has been singularly satisfactory. A failure of one or more of the ganged applicators caused assembly-line shutdowns. Moreover, the probability of at least one failure was quite high. The attempt to use a multiple spray head with a single applicator is also not satisfactory in that it is very difficult to achieve consistent adhesive flow through the multiple head. As a result, most presently known multiple-line applicators utilize the inherently disadvantageous air-operated applicator. The inventor herein knows of no prior art whereby an airless, solenoid-operated applicator is used in conjunction with closely-spaced multiple-line applications.
Accordingly, a primary object of the present invention is to provide multiple outlet adhesive applicator apparatus which applies closely-spaced lines or dots of an adhesive which is not operated by compressed air.
Another object of the present invention is to provide multiple outlet adhesive applicator apparatus which is capable of applying high viscosity, hot-melt adhesives by fast-acting applicators with precision, accuracy and repeatability.
Still another object of the present invention is to provide multiple outlet adhesive applicator apparatus for either cold or hot-melt adhesives which is directly solenoid actuated.
Still another object of the present invention is to provide multiple outlet adhesive applicator apparatus which allows for quick replacement of one or more of the multiple applicator outlets to reduce assembly-line down time.
A further object of the present invention is to provide multiple outlet adhesive applicator apparatus which is virtually leakfree and noncloggable.
Another object of the present invention is to provide multiple-outlet adhesive applicator apparatus which provides a means for filtering a liquid adhesive which allows for removal and replacement of a filter without disturbing any flow lines associated with the adhesive dispensing apparatus.
Another object of the present invention is to provide a flow arrangement for a multiple-outlet adhesive applicator which simultaneously supplies a heated, liquified adhesive to each of the multiple outlets.
Another object of the present invention is to provide multiple-outlet adhesive applicator apparatus which is capable of applying virtually any desired pattern of lines or dots of adhesive without regard to the physical limitation of the spacing between individual applicators.